Preparation of cyclopentadiene



Patented Mar. 23., 1948 PREPARATION OF CYCLOPENTADIENE Robert M. Kennedy, Drexel Hill, and Stanford J. Hetzel, Cheltenham, Pa., assignors to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey No Drawing. ApplicationFebruary 26, 1946,-

.Serial No. 650,394

2 Claims. 1

This invention relates to dehydrogenation and Specifically it recyclization of hydrocarbons. lates to the dehydrogenation and cyclization of n-pentane, l-pentene, 2-pentene and 1,3 pentadiene to 1,3 cyclopentadiene. More specifically, the'invention is concerned with a commercially feasible process for the conversion of n-pentane to 1,3 cyclopentadiene.

The conversion of pentane to 1,3 cyclopentadiene is considered to take place by way of, say, 1.-pentene and 1,3pentadiene. The yield of 1,3 cyclopentadiene will be higher when the charging stock requires the least amount of dehydrogenation. Accordingly, the invention will be described with reference to the conversion of 1,3 pentadiene to 1,3 cyclopentadiene to which it is pre-eminently suited. The reactions in the foregoing enumerated steps can be represented as follows:

--H Pentane HC-CH II II HO CH equivalent silicon carbides can be employed. The contact mass is preferably in a sub-divided state. Particles having a cylindrical shape and measuring 1 3' inch in diameter as well as length have been employed. Other sizes can be employed, the

essential condition being good contact between the hydrocarbon compound and the contact mass. Also, the contact mass should not cause too great a pressure drop through the conversion tube for practical operation reasons.

The temperature employed for the dehydrogenation of the hydrocarbon, in the instant case 1,3 pentadiene, will vary depending upon the other conditions of operation and on the nature or purity of the charging stock. However, the conversion of 1,3 pentadiene can be advantageously effected at a'temperature within the range 300 C. to a temperature above which substantial decomposition of the hydrocarbons will take place. More specifically a temperature within the range 400 (l-700? 0., preferably 450 C.- 650 C.. can be employed.

While the conversion per pass is substantially independent of pressure it has been found that lower pressures seem to form higher yields on recycling. Accordingly. while higher and lower pressures are not excluded from the scope of the invention, pressures in the range of 1000 mm. Hg-IO mm. Hg. preferably 200 mm. Hg-10 mm. Hg, can be employed.

Example 1' One thousand grams of 1.3 pentadiene were charged at a rate of 5 grams/minute, at a pres= sure of about 30 mm. Hgv to 1000 grams of a mass, consisting of silicon carbide, in a conversion tube at a, temperature of 600 C. The efiiuent from the conversion tube was cooled. condensed and fractionated. resulting in a yield of 39.0 grams of 1,3 cyclopentadiene. On recycle of the unconverted 1,3 pentadiene the yield is 440 grams.

Example 21 One thousand grams of 1,3 pentadiene were charged at a rate of 5 grams/minute, at a, pressure of about 15 mm. Hg, to 1000 grams of a mass, consisting of silicon carbide, in a conversion tube at a temperature of 610 C. The efiluent from the conversion tube was cooled, condensed and fractionated, resulting in a yield of 50.4 grams of 1,3 cyclopentadiene. On recycle oi the unconverted 1,3 pentadiene the yield is 4'75 It will be apparent tothose versed in the art the appended claims. the essence of the invention.

being that n-pentane, l-pentene, 2-pentene and/or 1,3 pentadiene can be dehydrogenated and cyclized by contacting the same at elevated temperature and suitable pressure with silicon carbide as set forth herein and in the appended claims.

What we claim and desire to protect by Letters Patent is:

1. A process for the dehydrogenation and cyclizatlon to 1,3 cyclopentadiene of 1,3 pentadie'ne which comprises subjecting said compound to a dehydrogenation temperature within the range 300' C. to a temperature above which sub: stantial decomposition of the hydrocarbons will take place in the presence of a contact mass consisting essentially of silicon carbide for a time suflicient to cause a desired extent of conversion to cyclopentadiene.

2. A process according to claim 1 wherein the temperature is within the range 450' C.-650 C. and the pressure is within the range 200 mm. Hg-10 mm. Hz.

ROBERT M. KENNEDY.. STANFORD J. HETZEL.

REFERENCES CITED The following references are of record in the 1 file of this patent:

UNITED STATES PATENTS OTHER REFERENCES -Wi1s0n, Jr. et al.; Chem. Rev., vol. 34; 2-4 0 (1944). Patent Omce Library.

"Frey at 9.1.; Jour. Ind. Eng. Chem, vol. 24, 282-7 (1932). Patent Ofllce Library, 

